1. Field of the Invention
The present invention relates to a system and method for providing improved event reading, data processing and system configuration capabilities in a flow cytometer. In particular, the present invention provides a system and method for use with a flow cytometer that enables the event reading components of the flow cytometer to capture and digitize substantially the entire optical waveform of each detected event, and provides improved, near real-time processing of the digitized waveform data and automated system configuration assessment capabilities.
2. Description of the Related Art
Flow cytometers known in the art are used for analyzing and sorting particles in a fluid sample, such as cells of a blood sample or particles of interest in any other type of biological or chemical sample. A flow cytometer typically includes a sample reservoir for receiving a fluid sample, such as a blood sample, and a sheath reservoir containing a sheath fluid. The flow cytometer transports the particles (hereinafter called xe2x80x9ccellsxe2x80x9d) in the fluid sample as a cell stream to a flow cell, while also directing the sheath fluid to the flow cell.
Within the flow cell, a liquid sheath is formed around the cell stream to impart a substantially uniform velocity on the cell stream. The flow cell hydrodynamically focuses the cells within the stream to pass through the center of a laser beam. The point at which the cells intersect the laser beam, commonly known as the interrogation point, can be inside or outside the flow cell. As a cell moves through the interrogation point, it causes the laser light to scatter. The laser light also excites components in the cell stream that have fluorescent properties, such as fluorescent markers that have been added to the fluid sample and adhered to certain cells of interest, or fluorescent beads mixed into the stream.
The flow cytometer further includes an appropriate detection system consisting of photomultipliers tubes, photodiodes or other light detecting devices, which are focused at the intersection point. The flow cytometer analyzes the detected light to measure physical and fluorescent properties of the cell. The flow cytometer can further sort the cells based on these measured properties.
To sort cells by an electrostatic method, the desired cell must be contained within an electrically charged droplet. To produce droplets, the flow cell is rapidly vibrated by an acoustic device, such as a piezoelectric element. The droplets form after the cell stream exits the flow cell and at a distance downstream from the interrogation point. Hence, a time delay exists from when the cell is at the interrogation point until the cell reaches the actual break-off point of the droplet. The magnitude of the time delay is a function of the manner in which the flow cell is vibrated to produce the droplets, and generally can be manually adjusted, if necessary.
To charge the droplet, the flow cell includes a charging element whose electrical potential can be rapidly changed. Due to the time delay which occurs while the cell travels from the interrogation point to the droplet break-off point, the flow cytometer must invoke a delay period between when the cell is detected to when the electrical potential is applied to the charging element. This charging delay is commonly referred to as the xe2x80x9cdrop delayxe2x80x9d, and should coincide with the travel time delay for the cell between the interrogation point and the droplet break-off point to insure that the cell of interest is in the droplet being charged.
At the instant the desired cell is in the droplet just breaking away from the cell stream, the charging element is brought up to the appropriate potential, thereby causing the droplet to isolate the charge once it is broken off from the stream. The electrostatic potential from the charging circuit cycles between different potentials to appropriately charge each droplet as it is broken off from the cell stream.
Because the cell stream exits the flow cell in a substantially downward vertical direction, the droplets also propagate in that direction after they are formed. To sort the charged droplet containing the desired cell, the flow cytometer includes two or more deflection plates held at a constant electrical potential difference. The deflection plates form an electrostatic field which deflects the trajectory of charged droplets from that of uncharged droplets as they pass through the electrostatic field. Positively charged droplets are attracted by the negative plate and repelled by the positive plate, while negatively charged droplets are attracted to the positive plate and repelled by the negative plate. The lengths of the deflection plates are small enough so that the droplets which are traveling at high velocity clear the electrostatic field before striking the plates. Accordingly, the droplets and the cells contained therein can be collected in appropriate collection vessels downstream of the plates.
Known flow cytometers similar to the type described above are described, for example, in U.S. Pat. Nos. 3,960,449, 4,347,935, 4,667,830, 5,464,581, 5,483,469, 5,602,039, 5,643,796 and 5,700,692, the entire contents of each patent being incorporated by reference herein. Other types of known flow cytometer, are the FACSVantage(trademark), FACSort(trademark), FACSCount(trademark), FACScan(trademark) and FACSCalibur (trademark) systems, each manufactured by Becton Dickinson and Company, the assignee of the present invention.
Although the flow cytometers described above can be suitable for reading events as intended, these existing systems do suffer from certain drawbacks. For example, in these types of instruments, the controller or central processing unit (CPU) does not ordinarily process the data obtained from reading the events in xe2x80x9creal timexe2x80x9d. However, it is desirable to process the data in real time or near real time to improve the efficiency of the flow cytometer and the ability to compare the readings of the events on a real-time or near real-time basis.
These existing systems also do not capture the entire image of the event. That is, when each event is read by detecting, for example, light fluorescing from the cell or particle of interest, these systems capture the xe2x80x9cpeak pointxe2x80x9d or peak intensity of the detected light. These systems also typically measure the duration during which the light is detected. By detecting these two parameters, the existing systems can use this data to determine characteristics of the event, such as the identity and size of a cell of interest. However, these techniques do not enable the existing systems to sample individual regions of the cell or particle of interest, nor are they capable of being performed on a real-time or near real-time basis. Furthermore, these systems are typically incapable of comparing data from multiple events effectively and in a real time or near real-time manner.
In addition, these types of existing systems do not provide a mechanism that indicates the configuration of the system to the operator effectively. For example, these types of systems are typically configured with multiple detector and filter arrangements that enable the different detectors to detect light having wavelengths within different wavelength regions. In such an arrangement, one detector can detect light with having a wavelength within the range of blue light, for example, while another detector can detect light having a wavelength within the range of green light. However, if an incorrect filter is placed in front of a particular detector, the detector will detect the incorrect light (e.g., green light instead of blue light). The system will therefore give erroneous results. However, the operator of the system will have difficulty determining which filters are arranged incorrectly, and in the worst case, the error may go unnoticed.
Accordingly, a need exists for an improved system and method for use with a flow cytometer to improve the event reading and data processing features of the flow cytometer to eliminate the above drawbacks.
An object of the present invention is to provide a system and method for use with a flow cytometer to improve event reading and data processing capabilities of the flow cytometer, while also providing efficient system configuration assessment capabilities.
Another object of the present invention is to provide a system and method that enables a flow cytometer to capture and sample an entire waveform representative of an event being read, and which provides improved processing and analysis of the sampled data in a real-time or near real-time basis.
A further object of the present invention is to provide a system and method that is capable of indicating the configuration of a flow cytometer to an operator in an efficient and effective manner.
These and other objects are substantially achieved by providing a system and method for processing at least one signal representative of an event detected by at least one detector in a flow cytometer. The system and method employs a sampling device which is adapted to receive portions of the signal from the detector in time sequence and to generate a respective value representative of the respective magnitude of each respective portion of the signal as the respective portion of the signal is being received. The system and method further employ a storage device which is adapted to store the values generated by the sampling device. The sampling device can receive substantially all of the signal, and can generate the values which represent the portions of substantially all of the signal. The signal can be an analog signal representative of a light signal emitted from the event as detected by the detector. The system and method can further employ an arithmetic device which is adapted to, for example, subtract a designated value from each of the values generated by the sampling device. The designated value can be representative of an unwanted signal, such as crosstalk, detected by the detector, or can be representative of a characteristic of the detector. The sampling device can further be adapted to receive portions of a second signal from a second detector in time sequence and to generate a respective second value representative of the respective magnitude of each respective portion of the second signal as the respective portion of the second signal is being received, and the storage device can store the second values generated by the sampling device. The sampling device can receive the portions of the signal at a time different from that during which it receives at least some of the portions of the second signal, and the system and method can employ a comparator which is adapted to compare each of the second values with a respective one of the values to compare the signal to the second signal.
These and other objects are further substantially achieved by providing a system and for identifying a configuration of a detector unit of a flow cytometer. The system and method employ a port which is adapted to couple to a removable device that includes an optical clement, such as a mirror or filter, and a memory adapted to store information pertaining to the optical element. The system and method further employ a reader which is adapted to read the information stored in the memory when the removable device is coupled to the port. The system and method can also employ an indicator which adapted to provide an indication of the information read by the reader.
These and other objects are also substantially achieved by providing a removable device which is adapted for coupling with a port of a flow cytometer, and comprises an optical element, such as a filter or mirror, and a memory adapted to store information pertaining to the optical element.